An important objective in the advancement of integrated circuit (IC) technology is the scaling-down of IC dimensions. Such scaling-down of IC dimensions reduces area capacitance and is critical to obtaining higher speed performance of integrated circuits. Moreover, reducing the area of an IC die leads to higher yield in IC fabrication. Such advantages are a driving force to constantly scale down IC dimensions.
As the density of integrated circuit structures continually increases, the distance between the interconnect structures decreases. As the distance between the interconnect structures decreases, a dielectric material with a low dielectric constant (i.e., a low-k dielectric material) is desired for the insulating layer. The insulating layer being comprised of the dielectric material with a low dielectric constant results in lower capacitance between the interconnect structures. Such lower capacitance results in higher speed performance of the integrated circuit and also in lower power dissipation. In addition, such lower capacitance results in lower cross talk between the interconnect structures. Lower cross talk between interconnect structures is especially advantageous when the interconnect structures are disposed closer together as device density increases.
One example of a dielectric material with a low dielectric constant for the insulating layer is a porous dielectric material having pores throughout. One type of porous low-k dielectric material is formed from a low-k precursor material comprised of a thermosetting host material and a thermally degradable porogen material. In that case, a solution of the uncured, low-k, precursor material is applied by a spin-on process, and then a thermal process is performed for curing the low-k precursor material to form the porous low-k dielectric material. The thermal process causes curing of the low-k precursor material with cross-linking of the host material to form a low-k dielectric matrix and concurrently with phase separation of the porogen from the host material. The phase-separated porogen collects in nanoscopic domains within the host material and thermally decomposes into volatile by-products (i.e., porogen fragments) that diffuse out of the low-k dielectric material leaving nanopores in their place.
Integration of porous dielectrics into conventional device fabrication schemes has created new problems. The open and interconnected porosity of the dielectrics allow reactive gases and chemicals to easily penetrate into the porous structure and damage the bulk material. Particularly degrading processes are photoresist removal and metal deposition. Moreover, the introduction of nanopores drastically deteriorates the mechanical properties of the film thereby limiting the yield of chemical mechanical polishing in copper-ELK (extreme low-k dielectric) process integration.
To overcome these issues, a new integration approach is needed in order to realize the full advantages of low-k, porous dielectrics.